The primary goal of this project is to conduct a long-term clinical investigation of a simple and very effective method for the prevention of radiation caries. A second goal is to compare two modalities of delivery of the proposed approach, one that requires a limited amount of subprofessional work and time; the other that requires essentially no subprofessional work and time. Specifically, the project aims at confirming if the use of fluoride and chlorhexidine can: (1) prevent radiation caries; (2) prevent the bacterial shifts that accompany radiation-induced xerostomia; (3) promote the remineralization of existing or forming lesions; (4) contribute to maintain good gingival health even in patients who, for treatment-related circumstances or neglect, do not maintain adequate oral hygiene; and (5) reduce the risk of postradiotherapy complications of infectious origin. Another aim is to determine if the simplicity of the delivery method encourages patient compliance, and if the method that has practically no manpower requirements is an effective as that needing some subprofessional effort. To achieve these aims 150 head and neck cancer patients to be treated with radiotherapy comprising the major salivary glands will be randomly divided into two groups. Group 1 patients will be given four topical applications with a 1% chlorhexidine digluconate (CHX)-1% sodium fluoride gel and rinse daily with a 0.2% CHX-0.05% NaF rinse. In Group 2 the same rinses will be used but no topicals will be applied. Periodic assessments will be conducted over a two-year period of caries, gingival and soft tissue condition, presence or absence of signs of remineralization and CHX staining, stimulated salivary flow, and composition of the plaque bacterial flora. Questionnaires will be administered semiannually to assess the patients' compliance with, and acceptance of, the proposed regimens. The proportion of postradiotherapy complications will be compared over a five-year period with that of patients treated previously in the same hospitals. It is expected that the results of this project will lead to a better method of preventing radiation carries -- and, by extension, other acute caries syndromes as well. The expected results, plus the simplicity of delivery, may also contribute to enhance the patients' quality of life as compared with the present methods.